preload on spindle bearing

[adryan]

I've got a question about the preload of the spindle bearings.

I've got a Rongfu 25 and changed the spindle bearings (30205 and 30206 tappered roller bearings)

When the mill turnes at high speed (2150rpm) the bearings gets slightly warm, not to much, however I can hear a rattling sound. I think I hear the bearing cages.
Does this mean the preload is to little?

I installed the bearings without oil. so I could very good feel if there was any slop on the setup. I tightened the nuts to have just a little preload and put the grease in the bearigs.

[Runner4404spd]

you may not have enough grease in the bearings. also the bearings will take a seat on the races and loosen up the close tolerances that were set. you might need to snug them up again.

[Chris D]

I have not worked on the spindle for my mill yet, but I suspect that the bearings are grease packed and not oiled. As such, after confirming this, you will need to pull those bearings back out and pack them properly with grease or they will fail pretty quickly.

Packing bearings with grease is a bit of a pain and it needs to be done correctly. Simply wiping them with grease is not the correct way. There are two methods I am aware of to pack bearings:

1) Pnuematic unit that forces the grease into the bearing under presure. These units can be purchased and can be costly.

2) The old fashioned way I learned way back in high school. Assuming you are right handed...

Place a glob of grease in the palm of your left hand

Hold the bearing in your right hand

Using a sort of scraping motion, force the edge of the bearing into the grease glob while pushing it towards your palm. The grease needs to enter the bearing at the ends of the rollers. As you push the bearing into your palm, the grease if forced in between the rollers. You continue to do this till the grease comes out the other end of the roller (and cage). Then rotate the bearing and repeat the process. Continue untill you go all the way around the bearing.

It takes a while - perhaps as much as 5 to 10 minutes to pack a bearing this way, but it is the only way I know of to make sure you get the grease inbetween the rollers and inside the cage where it needs to be. Just wiping grease against the rollers is not suffficient.

As for pre-load, this is something you will tweak a bit during the first couple of hours of running. The bearing should not get hot, it can run warm though, especially at high RPM. The temp difference between hot and warm is approximately

160 degrees F or more = hot
140 degrees F or less = warm

These are relative to touch and are approximate.

Chris

[Pres]

Originally Posted by adryan I installed the bearings without oil. so I could very good feel if there was any slop on the setup. I tightened the nuts to have just a little preload and put the grease in the bearigs.

Suggestion: Don't use grease!
It serves no worthwhile film strength increase but does generates alot more heat.

Use a lightweight synthetic oil (like mobil 1, 0W-20) to give minimal bearing drag & heat.
-or-
perhaps a drip feed could be simply done.
(an oil mist would be even better, but more of a mess)

Keep up the nice work.
Pres

[deemon]

Hello.
I'm from Poland and first of all sorry form ma languwage.

Actually, i,ve got a stupid question - have you got any build plans any metal lahes??
I,m impress for this lethe - mayby you put som draw this beauty??

[NC Cams]

I just stumbled across this thread.

Grease vs oil: Grease is merely oil with a thickening agent. Grease will tend to run a bit warmer than oil but that's not really all that bad. As the temp goes up, moisture/consensate tends to flash off which is good. An operating temp of 120-160F is not detrimental to the bearing. However, grease (like oil in a contained sump) does need to be changed after time. How often depends on how hot it got for how long and how comtaminated it gets.

Bearing noise: steel caged bearings do tend to make a bit more noise than those with plastic cages. This is disconscerting but not detrimental to typical performance.

HOWEVER, when you get into high speed operation, you get into a situation where the rollers start/try to "slew" out of position. At such time, the cages can start to crash into the rollers and rattle around - sort of a built-in deficiency in the design.

For high speed ball and cylindrical roller bearing use, plastic cages are often preferrable because you can more precisely "wrap" the rolling elements to guide them better. Being self lubing and quieter, plastic cages can actually perform better in such applications.

Even though the plastic cage has it's benefits, tooling and assembly costs preclude it's use in each and every application. Besides, if overheating is a possiblity, they can melt with heat over time. This is why machined brass and/or stamped steel are still used in a majority of the severe service, build and forget applications where MAX durability are expected.

Edit: bearing preload will affect temp rise - the higher the P/L the higher the temp rise and vice versa. With the spindle disconnected from drive (assuming it is NOT directly driven by motor) check the break away torque with an inch-pound beam style torque wrench.

10 or so lb-in is a reasonable starting value. You can probably go a bit higher for more stiffness and a bit lower for higher speed use to reduce temp rise.

Lowest friction/temp rise will occur with 0.000 to 0.005" measured BIDIRECTIONAL end play but this will probably chatter/rattle unacceptably when machining.

A very reasonable H/D grease would be a #2 viscosity car wheel bearing grease that is "Ford/Mercury moly fortified" - Valvoline sells it and you can get it at most auto parts stores.

After greasing, run at 10% speed until it reaches temp to evenly distribute/channel the grease. Subsequently, you can go to full speed range. On subsequent start-up, it will be good to run slow at first for few minutes before going at BANZAI speed.

[jderou]

You don't pack a spindle bearing with grease the way that you would a wheel bearing. They use very little grease. I have been told that a little rattle is normal at certain rpms, especially during break-in.

[frankg521]

on my mill bearings the inner race was moveing on the bottom i used locktite
retaining fluid now thier whisper quiet

Frank